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Old 17-01-2020, 18:44   #1
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DC to DC Converter vs Alternator upgrade

I'm looking for some input as I make the choice between adding a DC to DC converter or upgrading my existing alternator.
Last year I replace the lead acid batteries on my 1989 Pearson 34 with a 440 amp hour house bank (4 six volt, 220 amp hour, AGM batteries, in two banks, combined) and a starter battery. My existing alternator is a 55 AMP Hitachi with an internal regulator. The engine is a 3GM30C Yanmar. I run a 12 volt system.
My original plan was to go to a high output alternator, with an external regulator. The goal is to speed up charging times and avoid the potential for overcharging the AGM batteries.
My decision was complicated when a DC to DC charger was suggested as a less expensive way to achieve a similar result. I've looked at specs for both a Victron and a Sterling model. I must admit I don't understand the technology (how do you get more output with the input is still be the same??..).
Can anyone give me the pros and cons of the DC to DC vs. the high output alternator route?
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Old 17-01-2020, 19:22   #2
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Re: DC to DC Converter vs Alternator upgrade

First off if you have not already go pick up a copy of Nigel Calder's "Boatowner's Mechanical and Electrical Manual". If you read it cover to cover you will be many boat lengths ahead of most boat owners.

DC to DC converters are not sources of electrical power. They are used to convert one voltage of DC to another (e.g. 24 volts to 12 volts) and/or to isolate one circuit from another.

Sources of power include an (inverter/) charger, your alternator, solar panels and the like. Each of these sources has a maximum in terms of current that they can supply to charge your batteries.

So, running your 12 volt, 55 amp alternator into a DC to DC converter (with 12 volts output) will not get you any better charging rate.

Your best bet is to spec out an external regulated alternator and use that to charge your batteries.

Your 55 amp alternator is woefully lacking when it comes to charging your "new" house bank.

Take a look here:

https://marinehowto.com/automotive-a...cle-batteries/

MaineSail is a CF member and his website is a treasure trove of information.

Welcome to CF (hey, I had to get the jump on GordMay)
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Old 17-01-2020, 20:50   #3
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Re: DC to DC Converter vs Alternator upgrade

Note there is a huge set of differences between a DCDC converter, and a proper **charger** which is what you want.

The DCDC will cost a lot less unless you are DIYing the alt upgrade, rebuilt unit etc, belts and pulleys can get complicated and cost a lot.

But depending on factors, if you end up with capability of continuous charging at 200A and a good VR no DCDC required that's worth something.

A DCDC will only lower amps not increase.

You might get a continuous 35-40A from your current alt in hot conditions.

An external VR like Balmar MC-614 may be sufficient, no DCDC needed, the issue is getting the right voltage and hold time for Absorb, and (only after Full) dropping to Float.

Without the former you may never get Full, without the latter you may chronically overcharge.

Your starting point is discovering exactly what is actually going on now, need a decent ammeter and a bit more knowledge is all, before spending lots of money.
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Old 17-01-2020, 21:37   #4
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Re: DC to DC Converter vs Alternator upgrade

I don't wish to address the other errors in this posting - Just the one in bold. The statement is simply not true. It appears to show a profond lack of understanding of how DC to DC converters operate. Buck-Boost DC to DC converters are not simple linear regulators. Without going into inductors , H-bridges, et al, anytime the output voltage is lower than the input voltage there (with any common design) is a current increase. The input and output wattage (minus internal consumption) is the same.

Quote:
Originally Posted by john61ct View Post
Note there is a huge set of differences between a DCDC converter, and a proper **charger** which is what you want.

The DCDC will cost a lot less unless you are DIYing the alt upgrade, rebuilt unit etc, belts and pulleys can get complicated and cost a lot.

But depending on factors, if you end up with capability of continuous charging at 200A and a good VR no DCDC required that's worth something.

A DCDC will only lower amps not increase.

You might get a continuous 35-40A from your current alt in hot conditions.

An external VR like Balmar MC-614 may be sufficient, no DCDC needed, the issue is getting the right voltage and hold time for Absorb, and (only after Full) dropping to Float.

Without the former you may never get Full, without the latter you may chronically overcharge.

Your starting point is discovering exactly what is actually going on now, need a decent ammeter and a bit more knowledge is all, before spending lots of money.
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Old 17-01-2020, 21:44   #5
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Re: DC to DC Converter vs Alternator upgrade

I clearly stated I was not tslking about DCDC converters, and have no idea why anyone would in this context.

Seems in bad faith tbh.

All I meant, for a layman's (mis)understanding, is that a DCDC **charger** - which is not changing voltage much at all - will not extract 80A out of a 55A alternator

which is exactly what OP expressed confusion about.

In other words, the "finishing" faster goal does not come from a higher current rate.
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Old 17-01-2020, 22:16   #6
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Re: DC to DC Converter vs Alternator upgrade

Quote:
Originally Posted by john61ct View Post
I clearly stated I was not tslking about DCDC converters, and have no idea why anyone would in this context.
Odd, you posted about DC to DC converters vs proper chargers.

Quote:
Originally Posted by john61ct
Note there is a huge set of differences between a DCDC converter, and a proper **charger** which is what you want.
Here is a photo of a proper charger "VICTRON ENERGY SKYLLA-I 24/80 (1+1) 230VAC/45-65HZ"

If you meant a DC to DC converter with charging mode, colloquially known as a DC to DC charger, you should have stated such to avoid confusion.

It was clearly understood that the OP (who I hope we have not scared away) wants to get better charging with protection for his AGM bank.

Quote:
Originally Posted by john61ct
Seems in bad faith tbh.
sigh - once again you accuse someone else of bad faith. In this case the "bad faith" personal attack is directed to me. I should be insulted but I am not. I am a bit amused and I do find it ironic.

We have different ideas of what bad faith is. I find that changing the subject or ignoring questions asking you to state what experience you have or how you come about your recommendations is in bad faith.

To each their own.

Quote:
All I meant, for a layman's (mis)understanding, is that a DCDC **charger** - which is not changing voltage much at all - will not extract 80A out of a 55A alternator

which is exactly what OP expressed confusion about.

In other words, the "finishing" faster goal does not come from a higher current rate.
Huh? Now you are really confusing me.

"finishing" faster most assuredly comes from a higher charging current.

It appears to me that your 80 amp - 55 amp comment is adding more confusion to the thread.That information is really not germane.

But again that is just my opinion.
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Old 17-01-2020, 22:52   #7
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Re: DC to DC Converter vs Alternator upgrade

The distinction is between a DCDC converter and a DCDC **charger**.

As in Sterling, CTEK, Renogy, Kisae, Redarc etc and yes Victron just came out with one.

Used to ensure proper charging of a bank from dumb DC energy sources like stock alternators.

Always are current limiting, always have CC/CV/Float stages, usually have built in VSR and switchable from engine IGN.

These days increasingly include a solar controller.

DCDC chargers.

No one is talking about shore / AC mains powered chargers, aka rectifiers.

And completely different from DCDC buck/boost converters.

DCDC chargers get the bank to Full faster by keeping consistent voltage at Absorb setpoint, and lowering the current so the alt doesn't keep shutting down overheating.
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Old 18-01-2020, 02:16   #8
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Re: DC to DC Converter vs Alternator upgrade

Hardly, you spoke of a proper charger. Ask anyone and they will say a proper charger is a line powered device for charging your batteries. When talking about a DC powered charger they would specify that. I think that you mis-spoke.

As a side note: I really don't understand why anyone would list the names of a bunch of RV/Schoolie/offroad dc chargers in a cruising forum. (yes, I know Victron, Sterling et al)

This is what happens when one learns all one knows from datasheets and manuals with very little real-word training or experience. Simple misunderstandings, misreadings etc lead to pedantry and mistakes.

The prior post is a prime example. Let's start.

Quote:
Originally Posted by john61ct
Used to ensure proper charging of a bank from dumb DC energy sources like stock alternators.
This is a great quote. In the off-road/motorhome crowd it may be true. The engines alternator was tapped and used to charge the "secondary" battery which was used for house loads. This was unsatisfactory for a number of reasons and lead to undercharged secondary batteries.

Then came Dc to DC converters.

At first fixed voltage DC to DC converters were used to charge the secondary battery. They were never very satisfactory because with a fixed voltage of 14.4 volts or so they could overcharge the secondary battery. My dad had one and it was big and spendy. He switched to solar as soon as he could.

Only fairly recently have the output of DC to DC converters been given multistage charging algorithms. And marketing called them DC to DC chargers. This must be what you were speaking when you mis-spoke and called them proper chargers.

Quote:
Originally Posted by john61ct
Always are current limiting, always have CC/CV/Float stages, usually have built in VSR and switchable from engine IGN.
You will have to explain what you mean by always current limiting. And while you are at it explain the difference between current limiting and CC, both of which they must have. I don't think you really understand.

Quote:
Originally Posted by john61ct
No one is talking about shore / AC mains powered chargers, aka rectifiers.
Say what? Rectifiers? I don't mean to be insulting but I don't think you know what you are talking about. Or you are just tossing this BS in as a distraction if you do.

Quote:
Originally Posted by john61ct
And completely different from DCDC buck/boost converters.
And the wind cried Mary

Quote:
Originally Posted by john61ct
DCDC chargers get the bank to Full faster by keeping consistent voltage at Absorb setpoint, and lowering the current so the alt doesn't keep shutting down overheating.
I like this quote the best. At first glance it appear to make sense. But is you look closer you will see a number assumptions, a lack of depth of understanding and just some plain odd thinking that really makes it stand out.
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Old 18-01-2020, 02:58   #9
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Re: DC to DC Converter vs Alternator upgrade

Welcome to the forum Dave.

I presume you are referring to one of the alternator to battery chargers, these are DC to DC converters, but essentially function as an external alternator regulator without the need to modify the internal wiring of the alternator.

They do their job very well, but often the fundamental problem is the low output of the stock alternator. Many of the stock alternators rapidly overheat and cut their output back to prevent damage. Thus in reality they do not deliver anything like their rating would suggest.

The Alternator to battery chargers will use more appropriate and aggressive charge setting points which helps boost the alternator output, but they cannot improve the alternator cooling. If this is the limiting factor the gains are only small.

The Hitachi range of stock alternators fitted to the Yanmar engines have a poor reputation with only limited output. Upgrading the alternator is likely to to produce a more substantial improvement and would be the option I would take in your case.
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Old 18-01-2020, 03:52   #10
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Re: DC to DC Converter vs Alternator upgrade

Quote:
Originally Posted by noelex 77 View Post
Welcome to the forum Dave.

I presume you are referring to one of the alternator to battery chargers, these are DC to DC converters, but essentially function as an external alternator regulator without the need to modify the internal wiring of the alternator.

They do their job very well, but often the fundamental problem is the low output of the stock alternator. Many of the stock alternators rapidly overheat and cut their output back to prevent damage from overheating. Thus in reality they do not deliver anything like their rating would suggest.

The Alternator to battery chargers will use more appropriate and aggressive charge setting points which helps boost the alternator output but they cannot improve the alternator cooling. If this is the limiting factor the gains are only small.

The Hitachi range of stock alternators fitted to the Yanmar engines have a poor reputation with only limited output so upgrading the alternator is likely to to produce much more significant gains and would be the option I would take in your case.
That's the very thing.

A2B chargers can "trick" the alternator into full output by pulling down the voltage, then converting it up for the batts. But this is a fool's errand with a stock Hitachi (especially) and any other car-type alternator which is simply not designed for and is not suitable for bulk power production.

So start with the alternator. But it's not "either/or" ; you'll need proper regulation too.

But the good news is that this is the best investment you can make into your power system. It's very efficient and very convenient to be able to make good power every time you run your main engine and it's a lot cheaper than running a generator, if the main is on anyway.
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Old 18-01-2020, 08:16   #11
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Re: DC to DC Converter vs Alternator upgrade

Does anyone but Sterling make A2B?

They also make B2B, which works quite a bit differently, a leading example of the DCDC charger product category, user-custom adjustable setpoints being a big plus.

A2B is closer to a specialized add-on external VR, more a part of the alternator side.

The DCDC **chargers** can be considered more an add-on to the battery, can be used with any charge source, included in a removable powerpak for other uses as well as your boat, very flexible approach.

But more limited in the amps throughput per unit.

And they've been around a long time, but it's true lots more competition to Sterling's been appearing in recent years, and the growing use of LFP has been increasing awareness of their utility.

Here https://www.amazon.com/SMAKN%C2%AE-C.../dp/B00UYBL252

is an example of a low end DCDC **converter**, not current limiting, no stages, no termination algorithm, hence not a charge, you'd need to regulate the process manually.

A DCDC charger is a superset, includes converter circuitry.

Just as AC-DC mains chargers include rectification circuitry, is what distinguishes them from DCDC chargers.

(OT alert)
In the telecom and EV worlds, many high powered high voltage chargers and PSUs are referred to as rectifiers. Once you get up above 24V, an excellent source of top-notch gear for pennies on the dollar.

Many will in fact accept either DC input or AC mains.
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Old 18-01-2020, 08:25   #12
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Re: DC to DC Converter vs Alternator upgrade

Yes, a smaller alt won't provide as much power as a bigger one.

But increasing the **quality** of that output by just converting to a good external VR (or adding a DCDC charger) may well be enough of an improvement for a low-demand setup.

If not, either could continue to be used in an upgraded HO alt setup when that's done later.

The mechanical / infrastructure work getting brackets, multi-vee belts, pulley ratios, fatter wiring etc right is an area most owners need to bring in a pro, and can easily cost more than all the electrical components put together.
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Old 18-01-2020, 09:11   #13
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Re: DC to DC Converter vs Alternator upgrade

Quote:
Originally Posted by noelex 77 View Post
Welcome to the forum Dave.

I presume you are referring to one of the alternator to battery chargers, these are DC to DC converters, but essentially function as an external alternator regulator without the need to modify the internal wiring of the alternator.

They do their job very well, but often the fundamental problem is the low output of the stock alternator. Many of the stock alternators rapidly overheat and cut their output back to prevent damage. Thus in reality they do not deliver anything like their rating would suggest.

The Alternator to battery chargers will use more appropriate and aggressive charge setting points which helps boost the alternator output, but they cannot improve the alternator cooling. If this is the limiting factor the gains are only small.

The Hitachi range of stock alternators fitted to the Yanmar engines have a poor reputation with only limited output. Upgrading the alternator is likely to to produce a more substantial improvement and would be the option I would take in your case.
Me too
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Old 18-01-2020, 10:04   #14
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Re: DC to DC Converter vs Alternator upgrade

Hey all, thanks for the input... Good to see the distinction between a DC to DC Converter and a DC to DC Charger. Reading Sterlings marketing material on their charger, I was attracted by their claim:
"... The B2Bs have become extremely popular as they fast charge batteries as you cruise along without the need for complex wiring, touching your alternator, voiding the alternatorís warranty and tampering with the electronic control units (ECUs). You can provide the onboard batteries with a fast 4 stage charging profile with a very simple and speedy installation. All of the benefits of advanced charging without any of the draw backs. Simply connect the B2B between the battery being charged and the battery you wish to charge."

From your input, I'm concluding that I may get some improvement on both rate of charge and charge regulation, but am somewhat limited by the realities of the existing Hitachi alternator. The gold solution sounds like the Alternator upgrade, with an External Regulator. Be still my shuddering cheque book!!

BTW, great call out on Nigel Calder's book (or should I say sailors bible). My dog eared copy makes great winter reading up here in the frosty Great Lakes. Congrats to all who have actually read it in it's entirety "cover to cover"!!
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Old 18-01-2020, 10:56   #15
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Re: DC to DC Converter vs Alternator upgrade

If you are stuck with a "dumb" Yanmar Hitachi alternator - as I am and do not want to rebuild/change the alternator, you have the option to improve the cooling of the alternator and/or if necessary add a DC-DC charger.



The ambient temperature in the engine compartment can be quite high and as mentioned the output voltage will decrease due to the very rudimentary internal temperature compensation when the temperature rises in order to protect the alternator. The alternator will quickly heat up when charging at near to full capacity. Another factor is the tolerance of the output voltage might vary quite a bit from unit to unit and not fully charge your batteries even with a prolonged charging time.



If you can arrange forced air cooling from outside the engine compartment, from somewhere with a lower temperature like out on the deck, that will increase the alternator's performance and output voltage. Your engine will as well appreciate this if you only passively air feed the engine through a small diameter vent.



If your alternator has a too low output voltage even when cold to properly charge your batteries, your options are either to add an external regulator (a bit tricky for DIY on newer Hitachis) or add a proper DC-DC converter made for battery charging like Votronic 3326 Battery-to-battery charger VCC 1212-50 C85066. There are several similar products. Such a system will also limit the charging to the output settings of the converter so you can choose a product with somewhat lower output amperage than your alternator in order to protect the alternator. The latter is more important if you are charging LIFE batteries as they will take a much higher charging current than Lead acid batteries and potentially overheat your alternator quite fast.


If you go for a set up with a DC-DC I would charge the engine starter battery directly from the alternator and charge your house bank through the DC-DC.
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